FDCA (also known as dehydromucic or pyromucic acid), is a natural di-acid that is produced in the healthy human body at 3-5 mg quantities per day. Routes for its preparation using air oxidation of 2,5-disubstituted furans such as 5-hydroxymethylfurfural with catalysts comprising Co, Mn and/or Ce were reported recently in WO2010/132740, WO2011/043660 and WO2011/043661.
In GB 621971 polyesters and polyester-amides are prepared by reacting glycols with dicarboxylic acids of which at least one contains a heterocyclic ring, such as 2,5-FDCA. Under melt polymerization conditions, using sodium- and magnesium methoxide as a catalyst, FDCA dimethyl ester and 1.6 equivalents of ethylene glycol were reacted in a transesterification step at ambient pressure between 160 and 220° C., after which the polycondensation was carried out between 190 and 220° C. under 3 mm Hg pressure. The product had a reported melting point of 205-210° C. and readily yielded filaments from the melt. No additional properties were reported for PEF or other FDCA based polyesters in this 1946 document.
In HACHIHAMA, Yoshikazu the syntheses of Polyesters containing a Furan Ring are reported. In this paper polyesters are produced by condensation of 2,5-FDCA with various α,ω-glycols. According to this paper, ester interchange has proved to be the most convenient method for 2,5-furandicarboxylic acid polyesters, since the acid is difficult to be purified. The ester interchange reaction is promoted by the presence of a catalyst such as litharge, a natural mineral form of lead(II) oxide. The polymers made, however, were brown to greyish white.
The publication describes polyethylene-furandicarboxylate (PEF) with a melting point between 220 and 225° C., obtained using a lead catalyst. Also reported were the tri-, tetra-, penta- and hexamethylene diol polyester analogues with reported melting ranges of 115 to 120° C., 163 to 165° C., 70° C. and 143 to 145° C., respectively. For the ethylene glycol and 1,4-butanediol polyesters, fibre forming properties were reported. The polymers made were reported to be brown to greyish white.
In MOORE, J. A. polyesters derived from furan and tetrahydrofuran nuclei are described. Polymers were prepared using 2,5-furandicarbonyl chloride as monomer. As a result, polymers in the form of a white precipitate having a very low intrinsic viscosity (and hence low molecular weight) were obtained. In addition, a polymer was prepared from 1,6-hexane diol and dimethyl-2,5-furandicarboxylate, using calcium acetate and antimony oxide as catalyst. The number average molecular weight was low (less than 10,000), whereas the molecular weight distribution was relatively high (2.54 instead of about 2). Moreover, the product was greenish. Again, from this reference it would appear near impossible to produce polymers having a 2,5-furandicarboxylate moiety within the polymer backbone, at high molecular weight and without coloured impurities, without having to use a precipitation and/or purification step.
In WO 2007/052847 polymers are provided, having a 2,5-furandicarboxylate moiety within the polymer backbone and having a degree of polymerization of 185 or more and 600 or less. These polymers are made in a three step process involving the esterification of the 2,5-FDCA with a diol first using a tin catalyst and a titanium catalyst, and a second step involving polycondensation through an ester exchange reaction. The first step is carried out catalytically at a temperature within the preferred range of 150 to 180° C., whereas the polycondensation step is carried out under vacuum at a temperature within the preferred range of 180 to 230° C. The product is then purified by dissolving the same in hexafluoroisopropanol, reprecipitation and drying, followed by the third step, a solid state polymerization at a temperature in the range of from 140 to 180° C. Not disclosed, but found by the current inventors, is that the intermediate product produced by the process of this reference is darkly coloured. This is therefore the reason for the purification step. This essential purification step, and in particular when using hexafluoroisopropanol, is a serious drawback of this process, severely limiting the commercialization thereof. The problem vis-à-vis this recent development is to produce polymers having a 2,5-furandicarboxylate moiety within the polymer backbone, at high molecular weight and without coloured impurities, without having to use a purification step. Also polyesters from 1,3-propanediol and 1,4-butanediol were reported.
Conditions and reported properties of the 3 steps for the 3 polyesters are summarized in Table 1 below.
TABLE 1Experimental results from JP2008/291244conditionsconditions step 1conditions step 2step 3 (SolidMonomer(Esterification)(Polycondensation)Stating)Product propertiesEthylene280° C.; 4 hours280° C.; 6.5180° C.Mn = 23000;glycolhoursTm = 170° C.;Tg = 85° C.;Tc = 156° C.;Tdec = 332° C.1,3-230° C.; 4 hours230° C.; 6.5140° C.Mn = 15000;propanediolhoursTm = 150° C.;Tg = 39° C.;Tc = 102° C.;Tdec = 335° C.1,4-170° C.; 4 hours180° C.; 6.5150° C.Mn = 60000;butanediolhoursTm = 170° C.;Tg = 31° C.; Tc = 90° C.;Tdec = 338° C.
In JP2008/291244 a method for producing polyester resin including furan structure is provided. The method for producing a polyester resin including a furan structure comprises performing ester exchange reaction of a furandicarboxylic dialkyl ester component with a diol component, and then performing polycondensation reaction in the presence of a titanium tetrabutoxide/magnesium acetate mixed catalyst system. The molecular weight of the polyester resin leaves still much to desire, as does the polymerization time (7.5 hours) to achieve a reasonably high molecular weight.
In WO2010/077133 a tin catalyst was used for both the transesterification step and the polycondensation step. Although colour and Mn were better than any result reported at that time, the colour of the resulting resin in not good enough for application in bottles, fibres and films.
From the above references, it is clear that PEF has been known for more than 70 years and that many different recipes have been used in which temperatures, pressures, di-acid/diol stoechiometries, catalysts and precursors (di-acid or di-ester) have been varied.